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IC 


8929 



Bureau of Mines Information Circular/1983 



Economic Evaluation of Borehole 
and Conventional Mining Systems 
in Phosphate Deposits 

By Joseph A. Hrabik and Douglas J. Godesky 




UNITED STATES DEPARTMENT OF THE INTERIOR 



^i 



rf TJ/tvaA^ ii<^. BtvjAjut 



Information Circular -8929 



Economic Evaluation of Borehole 
and Conventional Mining Systems 
in Phosphate Deposits 

By Joseph A. Hrabik and Douglas J. Godesky 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



-w^ 



z<> 



UH 



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a,^Z\ 



This publication has been cataloged as follows: 



Hrabik, Joseph A 

Economic evaluation of borehole and conventional mining systems 
in phosphate deposits. 

(Bureau of Mines information circular ; 8929) 

Bibliography: p. 16, 

Supt. of Docs, no.: 1 28.27:8929. 

1. Phosphate mines and mining. 2. Borehole mining. I. Godesky, 
Douglas J. II. Title. III. Series: Information circular (United States. 
Bureau of Mines) : 892Q. 



TN295A]4 ITN913] 622s [622'. 3641 83-600001 



m '-i^.^ 



CONTENTS 

Page 

Abstract 1 

'^ Introduction 2 

, Acknowledgments 2 

r~ Resource availability 3 

I Deposit assumptions........... 3 

Borehole mining system 3 

nO Geologic considerations 6 

^ Conventional mining systems 6 

^ Benef iciation system 8 

~^^ Environmental considerations 8 

^ Economic evaluation 9 

(J Borehole mining capital cos t 11 

Borehole mining operating cost... 11 

Conventional mining capital cost 12 

Conventional mining operating cost 13 

Benef iciation system capital cost 14 

Benef iciation system operating cost 14 

Conclusions 14 

Suggestions for further investigation 15 

References 16 

Appendix A. — Mining and benef iciation parameters 17 

Appendix B. — Borehole mining system capital and operating costs 18 

Appendix C. — Conventional mining system capital and operating costs 20 

Appendix D. — Benef iciation system capital and operating costs 24 

Appendix E. — Cash flow analysis 25 

ILLUSTRATIONS 

1. Prototype borehole mining system 4 

2. Conventional mining systems 7 

3. Economic comparison — borehole mining versus conventional mining at 1.6 

million short tons of product per year 10 

4. Economic comparison — borehole mining versus conventional mining at 3.3 

million short tons of product per year 11 

5. Economic comparison — borehole raining versus conventional mining at 5.0 

million short tons of product per year 11 

TABLES 

1. Borehole mining system economic evaluation results 9 

2. Conventional mining system economic evaluation results 10 

rv] B-1. Estimated capital requirements, borehole raining system 18 

tx} B-2. Estiraated annual operating costs, borehole raining system 19 

^ C-1. Estiraated capital requirements, conventional raining systems 20 

^ C-2. Estimated annual operating costs, conventional mining system, at 1.6 

_ million short tons of product per year 21 

C-3. Estimated annual operating costs, conventional mining system, at 3.3 

million short tons of product per year 22 

.,„ C-4. Estimated annual operating costs, conventional mining system, at 5.0' 

dl million short tons of product per year 23 

D-1. Estimated capital requirements, benef iciation system 24 

D-2. Estimated annual operating costs, benef iciation system 24 



ii 



TABLES — CONTINUED 

Page 

E-1. Cash flow analysis at 50-ft overburden and 1.6 million short tons of 

product per year 25 

E-2. Cash flow analysis at 100-ft overburden and 1.6 million short tons of 

product per year 26 

E-3. Cash flow analysis at 150-ft overburden and 1.6 million short tons of 

product per year 27 

E-4. Cash flow analysis at 50-ft overburden and 3.3 million short tons of 

product per year 28 

E-5. Cash flow analysis at 100-ft overburden and 3.3 million short tons of 

product per year 29 

E-6. Cash flow analysis at 150-ft overburden and 3.3 million short tons of 

product per year 30 

E-7. Cash flow analysis at 50-ft overburden and 5.0 million short tons of 

product per year 31 

E-8. Cash flow analysis at 100-ft overburden and 5.0 million short tons of 

product per year 32 

E-9. Cash flow analysis at 150-ft overburden and 5.0 million short tons of 

product per year 33 

E-10. Cash flow analysis, borehole mining, at 230-ft overburden and 1.6 mil- 
lion short tons of product per year. 34 

E-11. Cash flow analysis, borehole mining, at 230-ft overburden and 3.3 mil- 
lion short tons of product per year 34 

E-12. Cash flow analysis, borehole mining, at 230-ft overburden and 5.0 mil- 
lion short tons of product per year. 34 





UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 


bhp 


brake horsepower 


psi 


pound per square inch 


ft 


foot 


rpm 


revolution per minute 


gpm 


gallon per minute 


scfm 


standard cubic foot 
per minute 


hp 


horsepower 










tph 


ton per hour 


h 


hour 










V ac 


volt, alternating 


in 


inch 




current 


kW-h 


kilowatt hour 


yd 


yard 


lb 


pound 


yd 3 


cubic yard 


lb/ft3 


pound per cubic foot 


yr 


year 


pet 


percent 







ECONOMIC EVALUATION OF BOREHOLE AND CONVENTIONAL MINING SYSTEMS 

IN PHOSPHATE DEPOSITS 

By Joseph At Hrabik and Douglas J, Godesky 



ABSTRACT 

The Bureau of Mines compared the feasibility of mining deep phosphate 
deposits by a borehole mining system with mining by proven conventional 
techniques. An economic comparison of the borehole mining system with 
conventional dragline and bucket wheel excavator mining systems was com- 
pleted at various mining depths and production rates. Hypothetical 
phosphate deposits, with various overburden thicknesses and reserve ton- 
nages, were defined. Geologic conditions necessary for the application 
of the borehole system were identified. Discounted cash flow analyses 
based on derived capital and operating costs were used to generate rates 
of return and product prices. 

Borehole mining was found to be more economical where overburden 
thickness was 150 ft or greater; however, at 50- and 100-ft thicknesses, 
conventional surface mining was more economical. Overburden thickness 
has a great effect on the economic feasiblity of the conventional mining 
systems but less effect on the economics of borehole mining. Economies 
of scale are only realized in conventional mining, since larger equip- 
ment is employed to achieve greater production, whereas increased pro- 
duction from borehole mining is achieved using additional equipment 
units. 

A comparison of the environmental effects of borehole and conventional 
surface mining systems showed that borehole mining is environmentally 
more desirable. 

^Mining engineer, Eastern Field Operations Center, Bureau of Mines, Pittsburgh, PA. 
^Physical scientist. Eastern Field Operations Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The phosphate mining industry of the 
United States is centralized in Florida 
where shallow sedimentary deposits have 
lent themselves to open pit mining. To- 
tal mining depths of less than 60 ft have 
made dragline mining the standard method 
of removing overburden and extracting 
phosphate ore (matrix) . In areas where 
thicker unconsolidated overburden is en- 
countered, dredges and bucket wheel ex- 
cavators can be employed to assist in the 
removal of overburden. 

As shallow phosphate reserves are de- 
pleted, deeper deposits are being consid- 
ered for development. Recovery of these 
deeper deposits by conventional surface 
mining methods would require the removal 
of thick overburden that could result in 
higher costs as well as increased envi- 
ronmental disturbance. Some of the deep 
deposits, such as those in northeastern 
Florida, are immediately overlain by beds 
of semiconsolidated to consolidated rock. 
Under these circumstances, borehole min- 
ing may be a technologically and econom- 
ically viable alternative to conventional 
mining. 

This Bureau of Mines study evaluates 
the economics of borehole and conven- 
tional mining systems as applied to the 
recovery of hypothetical phosphate de- 
posits. The extent of these deposits is 
assumed to be sufficient to justify capi- 
tal expenditures at various production 
rates. 

Borehole mining is a proposed method of 
recovering ore without overburden remov- 
al. The development of the borehole min- 
ing system for recovering a variety of 



minerals began early in the 20th century 
and continues to the present day. The 
most recent work was carried out by the 
Bureau of Mines under contract J0205038 
(4_).3 The applicability of the borehole 
mining system for recovering phosphate 
matrix was tested using the Bureau's 
experimental borehole mining equipment at 
Agrico Chemical Co.'s property in St, 
Johns County, Florida. A prototype bore- 
hole mining system with updated specifi- 
cations was designed as part of the con- 
tract, and is the basis for the borehole 
mining parameters and costs used in this 
study. The prototype system has not yet 
been built or tested. 

A beneficiation process is proposed to 
concentrate primary phosphate matrix sim- 
ilar to that found in northeastern Flor- 
ida. This high-grade phosphate matrix 
contains little pebble material and has a 
clay content averaging about 25 pet. 
Washing and double-stage flotation is 
proposed to produce a marketable phos- 
phate rock product. The beneficiation 
process is assumed to utilize advanced 
clay dewatering methods to reduce dis- 
posal area volume requirements. 

Results of the economic evaluation, 
at various mining depths and produc- 
tion rates , are graphically illustrated. 
These graphs can aid in the selection 
of a mining method whenever actual geo- 
logic conditions are similar to the hypo- 
thetical deposit situations depicted in 
this study. The graphs may also be help- 
ful in assessing the sensitivity of mine 
economics to depth and production rate 
variations. 



ACKNOWLEDGMENTS 



Thanks are extended to Dr. G. S. Knoke, 
research scientist. Flow Industries, 
Inc., Kent, WA, and Dr. G. A. Savanick, 
physicist. Bureau of Mines, Minneapolis, 
MN, for providing technical details and 
costing parameters of the prototype bore- 
hole mining system. Grateful acknowledg- 
ment is made to Mr. M. F. Dibble, mana- 
ger, new projects, Agrico Chemical Co., 



Tulsa, OK, and Mr. C. K. Brown, senior 
staff geologist, Agrico Chemical Co., 
Mulberry, FL, for their cooperation and 
technical assistance. Consultation with 
Mr. J. M. Williams, vice president and 

Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendixes. 



general manager, Zellars-Williams , Inc., 
Lakeland, FL, greatly contributed to the 



analysis of conventional 
alternatives. 



surface mining 



RESOURCE AVAILABILITY 



Phosphate deposits suitable for recov- 
ery by the borehole mining system are lo- 
cated at structurally and cyclically fa- 
vorable depositional sites along the 
southeastern coastal plain of the United 



States. The borehole mining system, if 
commercially applicable, could result in 
the recovery of billions of tons of phos- 
phate resources. 



DEPOSIT ASSUMPTIONS 



For the purposes of this evaluation, 
criteria for a set of hypothetical depos- 
its were established. Borehole and con- 
ventional dragline and bucket wheel min- 
ing systems were applied to the same 
criteria. 

All deposits described are hypotheti- 
cal and are not intended to accurately 
represent actual geologic, mining, or 
economic situations. The hypothetical 
deposits were constructed to serve the 
purposes of this study. 

The phosphate matrix was assumed to be 
20 ft thick and lying beneath either 50, 
100, 150, or 230 ft of overburden. The 
50 ft of overburden immediately above the 



phosphate matrix was assumed to contain 
consolidated carbonate beds and semicon- 
solidated materials. The upper portion 
of the overburden contained unconsoli- 
dated sand, shell fragments, and clay. 
The reserves were sufficient to support 
20-yr mine lives at production rates of 
1.6, 3.3, or 5.0 million short tons of 
product per year. 4 

The deposits were assumed to be later- 
ally extensive and consistent in quality, 
bed thickness, and depth. Such deposits 
are known to exist in parts of northeast- 
ern Florida at depths of 200 to 300 ft. 
Basic deposit assumptions are summarized 
in appendix A along with mine and mill 
operating parameters. 



BOREHOLE MINING SYSTEM 



Borehole mining is a method of recover- 
ing phosphate matrix without the removal 
of overburden. With the proposed bore- 
hole mining system, a borehole mining 
tool is lowered to the phosphate horizon 
through a predrilled, steel-cased bore- 
hole. A rotating water jet on the tool 
disintegrates the phosphate matrix while 
a jet pump at the lower end of the tool 
pumps the resulting slurry to the sur- 
face. The slurry is then transported to 
a beneficiation plant by pipeline. The 
resulting cavity is backfilled with waste 
material pumped back from the plant. 
Figure 1 illustrates a prototype borehole 
mining unit. Mining unit specifications 
and operating parameters are summarized 
in appendix A. 

The borehole mining tool is composed of 
mining, standard, and Kelly sections. 



The mining section, which houses the cut- 
ting jet and jet pump, operates within 
the phosphate horizon. Standard sections 
contain the pipes that deliver water and 
air down to the mining section and carry 
slurry up to the surface. A Kelly sec- 
tion with a three-passage swivel directs 
the water, air, and slurry flow through 
the top standard section. All sections 
are approximately 20 ft long and 8 in. in 
diameter. The overall length of the tool 
can be adjusted by the addition or remov- 
al of standard sections, which are in- 
stalled between the Kelly and mining 
sections. 

^Production values are rounded for text 
reporting purposes. Precise production 
values used in cost calculations are 
1,666,590, 3,333,180, and 5,000,135 short 
tons of product per year. 



Tool sections 
Tool section storage racit 

Air compressor 

Turntable 
Vertical slurry pump 
Slurry to process p lant 

Slurry tank 

Electrical power box 
Water supply 



Hydraulic wincti 



Derrick 




Hydraulic power package 



Kelly 
section 



Motor starter box 



Vertical turbine 
water pump 




Cutting jet 



Borehole cavity 



FIGURE 1. - Prototype borehole mining system. 

(Coiirtesy Flow Industries, Inc.) 



Operations for borehole mining in- 
clude site preparation, borehole drill- 
ing, equipment set up, mining, back- 
filling, and reclamation. Each deposit 
will require site-specific mining proce- 
dures to maximize matrix recovery. 

During site preparation, bulldozers 
clear vegetation, level the mining areas, 
and establish access roads. The borehole 
drilling locations and sequence of mining 
the borehole cavities are then marked by 
a survey crew. 

Drill rigs, casing trucks, and a fork- 
lift truck are used to drill and case the 
production boreholes. Holes are drilled 
to the bottom of the matrix and cased 
from the top of the ore horizon to the 
surface. The prototype borehole mining 
tool described in this study requires a 



12-in-diameter cased borehole. A tight 
fit between the casing and competent 
strata above the matrix would be estab- 
lished through the use of mechanical or 
cement seals or expandable packing de- 
vices. This would prevent water from be- 
ing forced into the annulus between the 
casing and the drill-hole wall and erod- 
ing the cavity roof. 

Borehole drilling is conducted on a 
staggered grid pattern. Mining on a 
staggered grid pattern permits greater 
matrix recovery than mining on a square 
pattern while maintaining the same mini- 
mum spacing between boreholes. A 70-ft 
spacing between boreholes would effect a 
final barrier of 10 ft between mined-out 
cavities. Barriers must be maintained 
so that phosphate slurry is not washed 
into previously mined cavities. Mining 



recovery is estimated to be 66.6 pet. 
Future testing may demonstrate that min- 
ing recovery may be increased by modify- 
ing the shape of cavities or reducing the 
cavity spacing. 

The borehole mining unit, consisting of 
the mining tool, derrick, pumps, and re- 
mote controls, mounted on a crawler base, 
is positioned over a cased borehole. The 
mining tool components are bolted togeth- 
er and lowered to the phosphate horizon. 
A hydraulic winch attached to the top of 
the derrick lowers and raises the mining 
tool. 

Pumps and compressors on the mining 
unit deliver water and air through the 
Kelly and standard sections to the cut- 
ting jet and the jet pump. A single cut- 
ting jet operates at 1,200 psi to disin- 
tegrate the phosphate matrix and form a 
slurry. Air is directed out of the cut- 
ting jet nozzle creating a shield that 
improves the jet's penetration through 
the flooded cavity and increases cutting 
distance. The cutting jet slides verti- 
cally within the mining tool to reach ma- 
trix from the base to the roof of the 
phosphate horizon. A turntable on the 
surface rotates the tool 360° during min- 
ing. Slurry flows to the jet pump in- 
takes at the lower end of the mining sec- 
tion and is pumped to the surface. At 
the surface, the slurry is transported to 
the benef iciation plant by pipeline. 

Matrix surrounding the cavity may 
slough in toward the mining tool as slur- 
ry is removed. Material would lie at an 
undetermined angle of repose from the 
bottom of the cavity near the jet pump to 
the outer perimeter of the cavity. The 
final cavity would be bowl-shaped with an 
average radius of 30 ft. 

Application of the borehole mining tool 
would not be limited by depth. The high- 
er ground water pressure associated with 
a deeper deposit would assist in the 
pumping of slurry to the surface. Minor 
adjustments of pumping power would be re- 
quired to overcome the additional fric- 
tion between the slurry and the standard 
section pipeline when mining depth is 
Increased. 



Most of the water used in mining, 
slurry transportation, and benef iciation 
would be recycled. A small portion of 
the water used would be lost owing to 
evaporation. The borehole cavities would 
receive ground water inflow to partially 
balance water loss in the other parts of 
the system. Only small quantities of 
deep-well, makeup water would be needed. 

After approximately 50 h of mining, 
the solids content of the slurry drops, 
indicating that the borehole cavity is 
mined out. The borehole tool is then 
withdrawn from the hole. Sections are 
separated and stored on a vertical rack. 
The mining unit is then moved to the next 
borehole location and the tool is again 
lowered to the phosphate bed. Total time 
required to withdraw the tool, move, and 
lower the tool down the next borehole 
varies from 3 to 5 h depending upon hole 
depth. 

One person operates each mining unit 
with extra personnel available to with- 
draw the tool and help move it between 
boreholes. A maintenance crew performs 
all maintenance and repair work and keeps 
a stock of spare parts and supplies on 
hand. Supervisors manage the mining, 
plan the moves, monitor progress, and 
keep the operation fully staffed and in 
production. One supervisor would be 
required to manage six direct labor 
employees . 

Clay and sand tailings would be gen- 
erated during the benef iciation process. 
Dewatered clay and sand tailings are com- 
bined and pumped from the benef iciation 
plant to the mining area where a backfill 
rig refills the borehole cavities O ) . 
Backfilling reduces or eliminates the 
possibility of surface subsidence and 
provides a means of disposing of both the 
clay and sands. 

The higher density clay-sand mixture, 
when introduced below clear water, does 
not mix with overlying water. The dis- 
posal of the wastes into the borehole 
cavity displaces relatively clear ground 
water, which would subsequently be recov- 
ered from the top of the borehole and re- 
circulated for plant use. 



In the final stages of backfilling, the 
steel casing is pulled from the hole and 
reused. The Florida Department of Envi- 
ronmental Regulations currently requires 
concrete sealing of the borehole with the 
steel casing in place. The department 
has waived this requirement for future 
borehole mining experiments. 

Reclamation following borehole mining 
would be minimal when compared with 
that required for surface mining opera- 
tions. Minor regrading and scarifying 
would be done by bulldozers , followed by 
revegetation with natural grasses and 



shrubs. As in conventional surface min- 
ing, approximately three growing sea- 
sons of reclamation area maintenance 
would be required to assure successful 
revegetation. 

The capacity of the proposed borehole 
mining unit is assumed to be 50 short 
tons of matrix per hour. Higher produc- 
tion can be achieved by increasing the 
number of mining units. Economies of 
scale do not apply to this system because 
different capacity tools have not been 
developed. 



GEOLOGIC CONSIDERATIONS 



The phosphate industry in the Southeast 
is currently surface mining phosphate de- 
posits with overburden thicknesses of up 
to 110 ft. Such overburden consists of 
unconsolidated sand and clay with no com- 
petent beds. Initial tests conducted for 
the Bureau indicated that for the suc- 
cessful application of borehole mining, a 
relatively competent rock bed must imme- 
diately overlie the phosphate matrix. A 
coiiq)etent bed prevents contamination of 
the matrix with sand and clay overburden 
that would otherwise cave into the bore- 
hole cavities. 

Primary phosphate deposits, those with 
no secondary reworking, facilitate mining 
by the borehole method. Primary deposits 
are very uniform in occurrence, quality, 
and thickness , which makes exploration 
data easier to interpret and mining easi- 
er to plan. This results in less explo- 
ration drilling. Since primary deposits 



contain only minor quantities of pebble, 
a more pumpable slurry results and the 
performance of the slurry pumping system 
is improved. 

While conclusive experiments have not 
been run, clay lenses within the matrix 
are believed to break up and then fall to 
the cavity floor as the matrix is mined; 
the larger fragments would then accumu- 
late on the cavity floor. This action 
would reduce the actual clay content of 
the material elevated to the surface and 
improve the overall phosphate grade of 
the recovered matrix. 

The grain size of the matrix particles 
and other primary depositional features 
of the bed may influence the shape of the 
borehole cavities. Owing to depositional 
variations, borehole cavities may assume 
irregular, noncircular shapes. 



CONVENTIONAL MINING SYSTEMS 



The hypothetical deposits described in 
this study can also be recovered by 
conventional mining technology. The sur- 
face mining system employed depends upon 
the thickness and character of the over- 
burden. Various overburden situations 
are addressed in three generalized cases. 
A cross section illustrating the three 
case situations is shown in figure 2. 



Site preparation work would be required 
in all three cases. Clearing vegetation, 
building access roads , and leveling min- 
ing areas would be accomplished by 
bulldozers. 

In case 1 , the 20-f t phosphate bed is 
overlain by 50 ft of interbedded carbon- 
ates, sands, and clays. A dragline 



V^MlWrnWiifc 



Surface 

3^5F 




Unconsolidated sand and clay 
to be removed using bucket wheel 
excavators 



Unconsolidated sand and clay and 
semi consolidated material to be- 
removed by dragline 



50ft 



Consolidated limestone interbedded 
with semi consolidated materials- 
to be removed by dragline 






"""^s^^^^s^BMSMMSS^M 



50ft 



0,.^. -^ 

1^^^^' 



y?? k%k 'J ^" '-^- 



^mis^^^Sl^^P 



' '^s'^oVO'-rtRy^ ^ - 



'?i?.2a 



^^^i^^^^^fe^ 



' ' ' "^ 



Phosphate matrix to be removed by 20^^ 
dragline j 




?^aa^ 



Case 3 



FIGURE 2. = Conventional mining systems. 



(Not to scale) 



removes this overburden and casts it into 
a previously mined cut to expose the 
phosphate matrix. The same dragline ex- 
cavates the matrix and transfers it to a 
slurry pit. In the slurry pit, water 
jets break, up the friable ore, creating a 
slurry that is pumped to a benef iciation 
plant. 

For case 2, an additional 50 ft of 
semlconsolidated overburden lies above 
the case 1 overburden, resulting in a to- 
tal overburden depth of 100 ft. A drag- 
line operating from the surface removes 
overburden and mines the matrix as de- 
scribed in case 1. 

For case 3, 50 ft of unconsolidated 
sand and clay lies above the case 2 over- 
burden, resulting in a total overburden 
depth of 150 ft. The top 50 ft of over- 
burden is stripped by two bucket wheel 
excavators, conveyed around the pit, and 
spread over mined out areas by stacker- 
reclaimers. Removal of the semi- 
consolidated overburden and phosphate 
matrix recovery proceeds as described in 
case 1. 



Reclamation involves casting overburden 
into mined-out cuts along with waste 
material from the benef iciation plant. A 
mixture of thickened clay slimes and sand 
tailings from the benef iciation plant is 
transported by pipeline to the mining 
area and backfilled into mined-out cuts. 
Draglines or dozers cover the waste with 
overburden material. Reasonable ground 
stability is expected since the amount of 
dewatered slimes and tailings is small 
compared with the amount of overburden 
cover. Topsoil is spread over the re- 
graded areas. The reclaimed land is 
suitable for agriculture or pasture. The 
ground surface would be stable enough to 
support most residential and industrial 
construction. 

Each case was evaluated at various 
production rates. Economies of scale 
are anticipated since draglines and 
bucket wheel excavators are available in 
different sizes. Conventional mining 
operating parameters are suimnarized in 
appendix A. 



BENEFICIATION SYSTEM 



The benef iciation processes for the 
primary phosphate matrix produced by 
borehole mining and conventional mining 
are identical. The operating parameters 
and recovery rates for benef iciation are 
based upon metallurgical tests. 

The major steps of the benef iciation 
process are washing and flotation. Wash- 
ing removes the clay fraction transport- 
ed with the matrix, A double-stage 
flotation circuit upgrades the washed 
feed. The grain size of feed is consist- 
ent, with 95 pet in the minus 35- to 
plus 200-mesh range. Owing to the grain 
size and high feed grade, 92 pet phos- 
phate recovery is achieved in the double- 
float circuit. Since some phosphate is 
lost in the washing circuit, an overall 



phosphate recovery of 85.7 pet is expect- 
ed. The resulting product output ton- 
nage equals about 46 pet of matrix input. 
The general operating parameters for the 
benef iciation system are summarized in 
appendix A. 

Waste clays produced during washing are 
thickened in clay holding ponds con- 
structed near the plant. Advanced de- 
watering methods are employed to minimize 
the pond retention time. It is assumed 
that 1 yr of clay settling capacity would 
be required. 

Thickened clay slimes are combined with 
sand tailings from flotation, pumped to 
the mining areas , and backfilled into 
mined-out cuts or borehole cavities. 



ENVIRONMENTAL CONSIDERATIONS 



Surface mining of phosphate has been 
occurring in central Florida for more 
than 90 yr. Very rugged landscapes and 
large above-grade clay dewatering ponds 
mark the locations of unreclaimed surface 
mining operations , and regulations now 
require the reclamation of surface mining 
areas for agricultural and recreational 
uses. 

Borehole mining may become a more envi- 
ronmentally acceptable alternative method 
for recovering phosphate, since commer- 
cial application of the borehole mining 
system eliminates the need for the remov- 
al of overburden material. Actual land 
disturbance is limited to clearing of 
vegetation and minor leveling of mining 
areas. The need to backfill and grade 
spoil piles, and the associated costs, 
are eliminated. Site cleanup and revege- 
tation are the only reclamation proce- 
dures required. 

Phosphate benef iciation yields sand 
tailings and water-retentive clay waste 
(clay) materials. The clay in central 
Florida, prior to dewatering, occupies 
between 1.25 and 2.0 times more volume 
than the unmined phosphate matrix 
(^-^) . The resulting extra volume of 
waste material is currently stored in 



above-grade clay dewatering ponds for ex- 
tended periods of time. 

Traditional methods of disposing of 
wastes, especially clays, ^re now being 
discouraged. The Florida Department of 
Environmental Regulation (2^) currently 
takes the position that because the 
"storage of waste clays for long periods 
of time interferes with expeditious rec- 
lamation and above grade storage of clays 
takes otherwise useful land out of pro- 
duction and raises potential health and 
safety problems , below grade storage and 
rapid reclamation techniques are encour- 
aged." In the future, surface mining 
operations will employ additional mechan- 
ical and chemical methods to reduce the 
clay volume, mix the clay with sand tail- 
ings , and backfill the waste into mined- 
out cuts. In borehole mining the waste 
is backfilled into mined-out cavities. 
Long-term above-grade waste storage is 
thus avoided. 

Water used in borehole mining and 
benef iciation is recirculated within the 
system. A large quantity of water is 
made available through the clay dewater- 
ing process. Ground water, infiltrat- 
ing borehole cavities at a slow rate, 
would be pumped from the cavities in the 



slurry. Ground water forced out of the 
cavity during backfilling would be pumped 
to the benef iciation plant for use. It 
is assumed that sufficient water is gen- 
erated during clay dewatering and mining 
for use throughout the system. 

Earlier studies indicated that bore- 
hole mining has not affected local water 



tables (4_) . 
fers remained 
tal boreholes 
sealed. The 



To insure that the aqui- 
undamaged, the experimen- 
in St. Johns County were 
steel casings were left 
in place and the boreholes were sealed 
with concrete from the top of the cavity 
to the surface. If this procedure is 
required in a large-scale operation, 
operating costs would be prohibitively 



high. The cooperation of government 

agencies would be required to reevaluate 

the need for sealing and develop lower 
cost alternatives. 

Significant controversy exists concern- 
ing the health hazard associated with ra- 
don levels on reclaimed phosphate lands 
following surface mining. The borehole 
mining system would minimize this ex- 
posure. Since the overburden is not 
disturbed, a significant earth buffer 
would remain intact above unrecovered 
uranium-enriched phosphate strata between 
boreholes and benef iciation wastes that 
are backfilled into mined-out borehole 
cavities. 



ECONOMIC EVALUATION 



An economic evaluation of borehole and 
conventional mining systems at selected 
production rates of 1.6, 3.3, and 5.0 
million short tons of product per yearS 
was conducted at overburden depths of 50, 
100, 150, and 230 ft for the borehole 
system, and 50, 100, and 150 ft for the 
conventional system. The 230-f t over- 
burden depth represents mining conditions 
in northern Florida and the depth for 
which Flow Industries, Inc., and Agrico 

-'See footnote 4. 



Chemical Co. provided borehole mining 
data. Mine and mill capital and operat- 
ing costs were estimated for these pro- 
duction rates and deposit depths. 

Discounted cash flow analyses were used 
to generate rates of return and product 
prices based on 20-yr project lives (1). 
Details of the analyses are given in 
appendix E. The results of the economic 
evaluations of the borehole mining system 
are presented in table 1 and those of the 
conventional mining system are presented 



TABLE 1. - Borehole mining system economic evaluation results 



Overburden, 


Capital costs 


Operating 
costs ' 


Rate of 

return, 2 

pet 


Price 1 


ft 


Break 
even 


20-pct rate 




Mine | Mill 


Mine | Mill 


of return 



1,666,590 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 
230. 



$45,598,000 
46,094,000 
46,591,000 
47,385,000 



$36 
36 
36 
36 



,202,000 
,202,000 
,202,000 
,202,000 



111. 64 
12.40 
13.17 
14.39 



$1.70 
1.70 
1.70 
1.70 



19.32 
18.61 
17.89 
16.72 



$16.26 
17.08 
17.89 
19.20 



$30.74 
31.51 
32.28 
33.51 



3,333,180 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 
230. 



$91,357,000 
92,350,000 
93,343,000 
94,932,000 



$55 
55 
55 
55 



,122,000 
,122,000 
,122,000 
,122,000 



11.83 
12.60 
13.36 
14.59 



$1.59 
1.59 
1.59 
1.59 



20.91 
20.15 
19.39 
18.13 



$16.13 
16.96 
17.77 
19.08 



$29.08 
29.85 
30.61 
31.85 



5 , 000 ,135 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 
230. 



$137,151,000 
138,613,000 
140,103,000 
142,486,000 



$70 
70 
70 
70 



,518,000 
,518,000 
,518,000 
,518,000 



11.90 
12.67 
13.43 
14.66 



'Per short ton of phosphate rock product. 
2Discounted cash flow rate of return at $30 



$1.54 
1.54 
1.54 
1.54 



21.77 
21.01 
20.22 
18.92 



$16.06 
16.86 
17.67 
18.98 



$28.28 
29.03 
29.79 
31.02 



per short ton of phosphate rock product. 



10 



TABLE 2, - Conventional mining system economic evaluation results 



Overburden, 


Capital costs 


Operating 
costs' 


Rate of 

return, 2 

pet 


Price 1 


ft 


Break 
even 


20-pct rate 




Mine | Mill 


Mine | Mill 


of return 



1,666,590 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 



$59,161,000 

75,178,000 

126,053,000 



$36,202,000 
36,202,000 
36,202,000 



$5.09 

6.40 

12.60 



$1.70 
1.70 
1.70 



22.70 
19.87 
11.19 



$10.18 
12.19 
20.13 



$26.70 
30.17 
43.04 



3,333,180 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 



$113,733,000 
128,057,000 
210,129,000 



$55,122,000 
55,122,000 
55 , 122,000 



$4.39 
5.06 
9.40 



$1.59 
1.59 
1.59 



25.38 
23.86 
16.05 



$8.98 

9.94 

15.66 



$23.87 
25.51 
35.29 



5,000,135 SHORT TONS OF PRODUCT PER YEAR 



50. 
100. 
150. 



168,575,000 


$70,518,000 


$3.75 


$1.54 


26.96 


$8.04 


$22.32 


179,023,000 


70,518,000 


4.64 


1.54 


25.74 


9.14 


23.63 


287,725,000 


70,518,000 


8.24 


1.54 


18.38 


13.95 


32.05 



'Per short ton of phosphate rock product. 

^Discounted cash flow rate of return at $30 per short ton of phosphate rock product. 



in table 2. Mill capital and operating 
costs are also summarized in tables 1 and 
2. Operating costs do not include depre- 
ciation, depletion, and other noncash 
flow items. 

The cost of initial deposit explora- 
tion is not included in capital cost es- 
timations. Development of a uniform 
phosphate resource over a broad area 
usually involves exploratory drilling of 
low density. Initial exploration cost 
for a particular tract is therefore small 
relative to other capital investments 
and would be the same for both systems. 
Premining control drilling is included 
in the borehole and conventional mining 
operating costs. 

Legal, environmental impact statement, 
permitting, and interest costs are not 
included in the mine or mill capital cost 
estimations. Salvage values were esti- 
mated as 10 pet of the initial capital 
investments for plant and equipment. 
Straight-line depreciation of plant and 
equipment was employed. 

Working capital for the borehole, 
conventional, and benef iciation systems 
equals 90 days operating cost. 



All cost estimates are adjusted to 
January 1981 dollars using Bureau of 
Labor Statistics cost indexes. Eco- 
nomic comparisons of the mining sys- 
tems are illustrated in figures 3, 4, 
and 5. 





■ 1 ' ' ' ' 1 ' ' ' •— 


^\ 


■ 


\. 


■ 


^T^ 


^Borehole mining 


: \ 


: 


Conventional mining — ^ 


\ 


—1 : ^ .1 , , , 


\ 



50 100 150 200 

OVERBURDEN THICKNESS, ft 



250 



FIGURE 3. " Economic comparison— borehole 
mining versus conventional mining at 1.6 mil- 
lion short tons of product per year. Discounted 
cash flow rate of return at $30 per short ton of 
phosphate rock product. 



11 



20 



15 



Conventional mining 




Borehole mining 



50 100 150 200 25 

OVERBURDEN THICKNESS, ft 

FIGURE 4. ■ Economic comparison— borehole 
mining versus conventional mining at 3.3 mil- 
lion short tons of product per year. Discounted 
cash flow rate of return at $30 per short ton of 
phosphate rock product. 



30 



25 



20 



50 100 150 200 250 

OVERBURDEN THICKNESS, ft 

FIGURE 5. ' Economic comparison-borehole 
mining versus conventional mining at 5.0 mil- 
lion short tons of product per year. Discounted 
cash flow rate of return at $30 per short ton of 
phosphate rock product. 

BOREHOLE MINING CAPITAL COST 

Capital costs for the borehole mining 
system include land acquisition, the 
borehole mining units, miscellaneous 
mining equipment, and working capital. 
Details of the borehole mining capital 
cost are presented in appendix B. 



' ' ' ' 1 ' ' ' ' 1 ' 


■ 


\. 


.^Conventionol mining 


Borehole mining 


^'^^^^: 


, ... 1 .... 1 , 


. . . 1 . . . , 1 . . . . 



Land acquisition costs are based on an 
estimated cost of $1 per short ton of 
product recovered over the 20-yr life of 
the operation, thereby relating land val- 
ue directly to the value of the recovera- 
ble phosphate. 

When commercially available, a proto- 
type borehole mining unit, capable of 
operating at 230 ft of overburden, is 
estimated to cost $700,000. This cost 
represents a fixed cost for the surface 
unit, Kelly, and mining sections and a 
variable cost for the standard sections. 
The standard section length and cost 
vary with the mining depth. The total 
borehole mining unit cost is obtained by 
multiplying the single unit cost, based 
upon deposit depth, by the number of 
units required. The number of units re- 
quired is based upon the mine capacity, 
a mining rate of 50 short tons per hour, 
a utilization level of 24 h per day, and 
the effective availability of the min- 
ing unit, which varies with deposit 
depth. A 10-pct contingency cost is then 
added to the total mining unit capital 
cost. Borehole mining units are not re- 
placed during the life of the mine and 
are depreciated over the first 15 yr of 
operation. 

The miscellaneous mining equipment cost 
is based upon an estimated cost of 
$40,000 per unit multiplied by the number 
of units. A 10-pct contingency factor is 
then added. Miscellaneous mining equip- 
ment is replaced after 10 yr of opera- 
tion. Costs are depreciated over the 
first 8 yr of use. 

BOREHOLE MINING OPERATING COST 

Operating cost for the borehole mining 
system is composed of 14 cost elements 
and details are present in appendix B. 

Site preparation cost is estimated at 
$2,326 per acre. The acreage required 
for each operation is based upon the 
operating schedule, matrix density, and 
the mining recovery. 

Drilling, casing, and sealing cost in- 
cludes premining control drilling, bore- 
hole drilling, and borehole casing and 



12 



sealing costs. Control drilling is based 
upon a hole density of 0.4 hole per acre, 
deposit depth, and an estimated average 
cost of $3,50 per foot for core drilling 
and gamma ray logging. 

The operating labor cost is based on an 
estimated labor rate of $12 per hour, as 
applied to the number of employees and 
the operating schedule. 



Site reclamation cost, including cav- 
ity backfilling, is based on an esti- 
mate of $1.50 per short ton of material 
backfilled. 

The slurry transportation cost is based 
on an estimated cost of $0.18 per short 
ton-mile, multiplied by the tonnage of 
ore and waste transported and by the av- 
erage transportation distance. 



The annual support and maintenance la- 
bor costs are estimated to be 80 and 25 
pet, respectively, of the annual operat- 
ing labor cost. 

Supervisory labor costs are estimated 
as a percentage of the total annual oper- 
ating labor, support labor, and mainte- 
nance labor costs. The percentages used 
at the 1.6, 3.3, and 5.0 million short 
ton per year production rates are 20, 15, 
and 10 pet, respectively. 

Payroll benefits and payroll overhead 
cost elements are estimated as 30 and 40 
pet, respectively, of the total of all 
four labor cost elements. 

The prototype unit is estimated to 
require power for the cutting jet, 
slurry pump, and other smaller pumps, 
for a total of 2,400 bhp which includes 
a 300-bhp variance with mining depth. 
The estimated annual power cost equals 
$580,682 per unit plus a variable cost 
per unit of $332 per foot of total mining 
depth. 

The annual maintenance supply cost is 
estimated at $30,000 per unit, operating 
on a 330 day per year schedule. This 
cost is adjusted to the 365 day per year 
schedule and multiplied by the number of 
units required. 

The health and safety cost is based on 
an annual cost estimate of $190,000 per 
year for 10 units operating for 330 days 
per year. This cost is adjusted to the 
required number of units and proposed 
operating schedule. 



The fixed costs attributed to mining 
are estimated to be 85 pet of the total 
annual mineral severance tax, local tax- 
es, and insurance cost. Severance tax, 
after ad valorem tax credit and reclama- 
tion rebate, is estimated at $1.21 per 
short ton of product. Local taxes and 
insurance are estimated at $0.58 per 
short ton of product. 

The operating cost, per short ton of 
product, is then obtained by dividing the 
total annual operating cost by the annual 
product tonnage. 

CONVENTIONAL MINING CAPITAL COST 

Capital costs for the conventional min- 
ing system included land acquisition, 
mine equipment, draglines and bucket 
wheel excavators, and working capital. 
Details of the conventional mining capi- 
tal cost are presented in appendix C. 

Land acquisition costs are equal to the 
land acquisition costs for the borehole 
mining system at the same production 
rate. Although mining recovery is higher 
for the conventional system, and less 
acreage is required, the costs are equiv- 
alent since they are based upon $1 per 
short ton of product recovered over the 
life of the mine. 

Mine equipment and dragline and bucket 
wheel excavator costs are based on cost 
estimates developed by industry and pub- 
lished sources. Costing models were fol- 
lowed for all calculations involving 
draglines and related expenses (_7) . At 



13 



150-ft overburden depths, where bucket 
wheel excavators are required, separate 
additional capital costs are developed. 

Mine equipment costs include the sup- 
port equipment for the dragline and buck- 
et wheel excavation systems. Some ele- 
ments of the initial base mine capital 
cost estimates required adjusting accord- 
ing to the following formula: 

New mine capital cost 

= Base mine capital cost 

r New mine capacity 1 ^ '^ 
|_ Base mine capacity] 

This scaling formula is based upon the 
assumption that capital costs are expo- 
nentially related to production capacity. 

Dragline capital costs are based upon 
the number of draglines required, the 
dragline sizes, and equipment manufactur- 
er's suggested costs. The proposed over- 
burden depths and production rates deter- 
mined the quantity and size of the 
equipment. 

The total bucket wheel system cost is 
based upon an estimated system cost of 
$108,535,540 for moving 28.7 million bank 
cubic yards of overburden per year. This 
cost is scaled to the proposed production 
rates using the 0.7 exponential scaling 
formula. Costs of the bucket wheel ex- 
cavators, conveyor systems, and stacker 
reclaimers are estimated to be 90 pet of 
the total bucket wheel system cost and 
are allocated to the dragline and bucket 
wheel excavator cost category. The re- 
maining 10 pet is for support equipment 
and is attributed to the mine equipment 
cost category. 

Items included under mine equipment 
cost are replaced after the first 10 yr 
of production. They are depreciated over 
the first 8 yr of use. Draglines and 
bucket wheel excavators are not replaced 
during the 20-yr production periods. 
They are depreciated over the first 15 yr 
of operation. 



CONVENTIONAL MINING OPERATING COST 

Operating costs for the conventional 
mining systems are composed of 18 cost 
elements and details are presented in 
appendix C. The estimated dragline oper- 
ating costs and related expenses were 
calculated using cost models developed by 
Zellars-Williams , Inc. (_7). The bucket 
wheel excavator system annual operating 
costs are based upon known system costs 
scaled to the proposed production rates 
and other factors. 

The two most important controlling fac- 
tors in the cost evaluation are the phos- 
phate reserve grade and characteristics 
and the mine capacity. Matrix pumping 
distances and mine recovery are examples 
of miscellaneous factors considered in 
the cost model. 

The power cost element is composed of 
dragline, slurry pit, and pumping power 
requirements. A power cost rate of 
$0.0416 per kilowatt hour is used to ob- 
tain the total annual power cost. 

The outside services cost element is 
composed of mine site preparation costs 
plus reclamation costs. Mine site prep- 
aration and reclamation costs are esti- 
mated at $708 and $2,500 per acre, 
respectively. 

Matrix pipeline cost is estimated at 
$34 per foot. The cost of premining con- 
trol drilling, gamma ray logging, and 
core analysis is estimated at $3.50 per 
foot. A drilling density of 0.4 hole per 
acre is used. 

Severance tax, after ad valorem tax 
credit and reclamation rebate, is esti- 
mated at $1.21 per short ton of product. 
Local taxes and insurance are estimated 
at $0.54 per short ton of product plus a 
4-pct sales tax. 

The operating cost, per short ton of 
product, is then obtained by dividing the 
total annual operating cost by the annual 
product tonnage. 



14 



BENEFICIATION SYSTEM CAPITAL COST 

Capital costs for the benef iciation 
system included mill plant capital and 
working capital. Details are presented 
in appendix D. At each production rate, 
the benef iciation processes and associ- 
ated capital costs are equal for the 
borehole and conventional mining systems. 
Mill plant capital cost is estimated at 
$35,500,000 for a 1.6 million short ton 
per year plant. This cost is scaled to 
the other production rates using an ex- 
ponential scaling factor of 0.6 in the 
following formula: 

New mill capital cost 



product for a plant producing 1.6 million 
short tons per year. This estimate is 
reduced by the plant depreciation cost, 
with a final estimate being $1.43 per 
short ton of product (for power, labor, 
and reagents). 

Reagents are estimated to be 60 pet 
of this cost, while the power and labor 
cost category is estimated at 40 pet. 
The power and labor cost element is 
scaled to adjust for other proposed pro- 
duction rates. The scaling method used 
is based upon the assxamption that operat- 
ing cost is exponentially related to 
the production capacity of the mill. The 
formula used is 



= Base mill capital cost 



4 



New mill capacity 
Base mill capacity 



0.6 



BENEFICIATION SYSTEM OPERATING COST 

Operating costs for the beneficiation 
system included power and labor, rea- 
gents, and fixed costs. Details are pre- 
sented in appendix D. At each production 
rate, the beneficiation processes and 
associated operating costs are equal for 
the borehole and conventional mining sys- 
tems. Mill operating cost for power, 
labor, reagents, and depreciation is es- 
timated at $2.50 per short ton of 



New mill power and labor cost 
= Base mill power and labor cost 
r Base mill capacity" 



New mill capacity 



,J..3_ 



The fixed costs attributed to benefici- 
ation are estimated to be 15 pet of the 
total annual mineral severance tax, local 
taxes, and insurance cost. Severance 
tax, after ad valorem tax credit and 
reclamation rebate, is estimated at $1.21 
per short ton of product. Local taxes 
and insurance are estimated at $0.58 per 
short ton. 



CONCLUSIONS 



Based on the economic evaluation of 
the borehole and conventional mining sys- 
tems , borehole mining systems are eco- 
nomically superior for the recovery of 
deep bedded phosphate deposits. However, 
the recovery of shallow phosphate depos- 
its by conventional mining is econom- 
ically more attractive than by borehole 
mining. 

Conventional surface mining with 50 and 
100 ft of overburden is more economical 
(i.e., has a higher rate of return) than 
borehole mining at all three production 
rates examined. At 150 ft of overburden, 
borehole mining is economically superior 



at all production rates. Only the bore- 
hole mining system was evaluated at a 
230-ft overburden thickness. The eco- 
nomic attractiveness (as measured by rate 
of return) of the conventional mining 
systems falls rapidly between 100 and 150 
ft of overburden owing to significantly 
higher capital and operating costs. By 
extrapolating the data, rate of return 
for conventional mining with 230 ft of 
overburden is expected to be prohibitive- 
ly low, perhaps negative, at a product 
price of $30 per short ton. The borehole 
mining system maintains a high level of 
economic attractiveness at 150 and 230 ft 
of overburden. 



15 



Conventional phosphate mines in Florida 
typically achieve rates of return between 
15 and 20 pet. The operations evaluated 
in this study attain comparable levels 
of profitability except for low produc- 
tion conventional mining with 150 ft of 
overburden. 

Borehole mining is environmentally more 
desirable for recovering phosphate de- 
posits than conventional surface mining 
alternatives. The surface area disturbed 
at any time during borehole mining is 
minimal. Borehole mining recovers the 
phosphate matrix without disturbing the 



material overlying the ore. Reclamation 
work required to restore the surface 
after borehole mining is limited to minor 
regrading and revegetation. 

The borehole mining system is an eco- 
nomically and environmentally attractive 
method of recovering phosphate under cer- 
tain geologic conditions. With the in- 
creasing need to mine deeper phosphate 
deposits, development of borehole mining 
technology should progress and in the 
future may supply a significant share of 
the demand for phosphate. 



SUGGESTIONS FOR FURTHER INVESTIGATION 



1 . Exploration or evaluation of areas 
where borehole mining can be applied to 
recover phosphate. 



- Examine various mining tool diameters 
to find the optimum diameter tool and 
borehole. 



- Delineate phosphate potential in ar- 
eas where borehole mining can be applied. 

- Assess the potential of applying 
borehole mining to offshore phosphate 
deposits. 

2. Testing the application of bore- 
hole mining under various overburden 
conditions. 



- Improve maneuverability of the water 
jet nozzle to increase mobility and cut- 
ting radius. 

- Redesign mining tool to increase 
unit production and maximize mining 
recovery. Evaluate possible economies 
of scale if production rate per unit 
exceeds 50 short tons of matrix per 
hour. 



- Determine cavity roof competence 
needed to prevent cavity collapse. 

- Test application of borehole mining 
methods in areas with no relatively com- 
petent overburden. 

3. Improve mechanical efficiency of 
borehole mining equipment. 



- Determine possible borehole cavity 
shapes, sizes, and spacings; estimate 
associated mining recovery rates. 



- Evaluate to 
required between 
the ore zone. 



what extent a seal is 
the casing and top of 



16 



REFERENCES 



1. Davidoff , R. L. Supply Analysis 
Model (SAM): A Minerals Availability 
System Methodology. BuMines IC 8820, 
1980, pp. 14-15. 

2. Florida Department of Natural 
Resources. Florida Statutes. Chapter 
16C - 16: Mine Reclamation. Florida Di- 
vision of Resource Management, amended 
Oct. 6, 1980. 

3. Marvin, M. H, , G. S. Knoke, and 
W. R. Archibald. Backfilling of Cavi- 
ties Produced in Borehole Mining Opera- 
tions (contract J0285037, Flow Indus- 
tries, Inc.). BuMines OFR 4-81, 1979, 
78 pp.; NTIS PB 81-171308. 

4. Scott, L. E. Borehole Mining of 
Phosphate Ores (contract J0205038, Flow 



Industries, Inc.). BuMines OFR 138-82, 
August 1981, 215 pp.; NTIS PB 82-257841. 

5. Timberlake, R. C. Building Land 
With Phosphate Wastes. Min. Eng. , v. 21, 
No. 12, December 1969, pp. 38-40. 

6. U.S. Bureau of Mines, Staff. The 
Florida Phosphate Slimes Problem. IC 
8668, 1975, 41 pp. 

7. Zellars, M. E., and J. M. Williams. 
Evaluation of the Phosphate Deposits 
of Florida Using the Minerals Availabil- 
ity System (contract J0377000, Zellars- 
Williams, Inc.). BxiMines OFR 112-78, 
June 1978, 199 pp.; NTIS PB 286 648/ AS. 



17 



APPENDIX A. — MINING AND BENEFICIATION PARAMETERS 



Basic deposit assumptions 

Matrix thickness ft. . 

Matrix density Ib/f t3. . 

Average overburden density. .Ib/ft^. . 
Matrix grade, pet: 

Bone phosphate of lime ' 

P205- 

Pebble content of matrix pet.. 

Clay content of matrix pet.. 

Matrix "X"^ yd^.. 

U pet BPL = 0.458 pet P205. 
^Matrix per short ton of product. 



20 
88 



36.25 

16.59 



25 

1.84 



General operating parameters 

Recovery, pet: 

Washing 

Flotation 

Overall benef iciation 

Product grade, pet: 

Bone phosphate of lime ' 



Borehole mining unit — Specifications 



Operating shifts per day 

Utilization level h. 

Operating days per year 

Mine life yr. 

U pet BPL = 0.458 pet P2O5. 

and approximate operating parameters 



Average unit mining rate. . . .tph. . 50 

Tool rotation rate rpm. . 10 

Mining tool diameter in.. 8 

Standard section length ft.. 20 

Cutting jet: 

Flow rate gpm. . 1,000 

Pressure psl. . 1,200 

Power hp . . 1,000 

Electric motors (500 hp, 

2,300 V ac) 2 

Jet pump : 

Flow rate gpm. . 500 

Pressure psl. . 1 ,200 

Power (for 250-ft mining 

depth) hp. . 500 

Electric motor (500 hp) 1 

Air compressor: 

Flow rate scfm.. 1,500 

Pressure psi. . 250 

Power hp. . 400 

Electric motor (400 hp, 

2,300 V ac) 1 

Borehole and conventional mining parameters at three production rates 



Slurry pump: 

Discharge flow rate gpm.. 

Power hp. . 

Electric motor (150 hp, 

2,300 V ac) 

Slurry tank capacity gal.. 

Water tank capacity gal.. 

Hydraulic power package hp.. 

Hydraulic electric motor (200 hp, 

2,300 V ac 

Size of mining unit ft.. 

Approximate unit weight (tanks 



empty, no sections). 
Average cavity radius 
Cavity separation. . . . 
Borehole separation. . 

Operating factor 

Move and setup 



..lb. 
..ft. 
..ft. 
..ft. 
.pet. 
...h. 



93.1 
92.0 
85.7 

68.00 

31.14 

3 

24 

365 

20 



1,600 
150 

1 

500 

2,000 

200 



10 by 10 
by 30 

150,000 
30 
10 
70 
90 
3-5 



Annual product output, short tons. 



Borehole mining parameters: 

Dally product output short tons.. 

Dally matrix production do. . . . 

Mining units 

Area mined per year acres . . 

Total area mined in 20 yr do.... 

Mining recovery pet. . 

Conventional mining parameters: 

Daily product output short tons.. 

Daily matrix production do.... 

Number of draglines and capacity at — 

50-f t overburden 

100-f t overburden 

150-f t overburden' 

Area mined per year acres.. 

Total area mined in 20 yr do.... 

Mining recovery pet. . 

'Bucket wheel excavators used also. 



1, 


666,590 


3, 


333,180 


5, 


000,135 




4,566 




9,132 




13,698 




10,000 




20,000 




30,000 




10 




20 




30 




143 




286 




429 




2,860 




5,720 




8,580 




66.6 




66.6 




66.6 




4,566 




9,132 




13,698 




10,000 




20,000 




30,000 


1, 


35 yd3 


2. 


35 yd 3 


2, 


52 yd 3 


2, 


31 yd3 


3, 


41 yd3 


4. 


46 yd 3 


2, 


31 yd3 


3, 


41 yd3 


4. 


46 yd 3 




112 




224 




336 




2,240 




4,480 




6,720 




85.0 




85.0 




85.0 



18 



APPENDIX B. --BOREHOLE MINING SYSTEM CAPITAL AND OPERATING COSTS 
TABLE B-1. - Estimated capital requirements, borehole mining system 



Overburden, ft. 



50 



100 



150 



230 



1,666,590 SHORT TONS OF PRODUCT PER 


YEAR 




Acquisition ' 


$33,332,000 
7,047,000 

440,000 
4,779,000 


$33,332,000 
7,228,000 

440,000 
5,094,000 


$33,332,000 
7,410,000 

440,000 
5,409,000 


$33,332,000 
7,700,000 


10 mining units. ............. 


Miscellaneous mining 
equipment . .....••. .......... 


440,000 


Working capital2 


5,913,000 


Total 


45,598,000 


46,094,000 


46,591,000 


47,385,000 



3,333,180 SHORT TONS OF PRODUCT PER 


YEAR 




Acquisition '.......•......... 


$66,664,000 
14,093,000 

880,000 
9,720,000 


$66,664,000 
14,456,000 

880,000 
10,350,000 


$66,664,000 
14,819,000 

880,000 
10,980,000 


$66,664,000 
15,400,000 


20 mining units. ............. 


Miscellaneous mining 

equipment 

Working capital^ 


880,000 
11,988,000 


Total 


91,357,000 


92,350,000 


93,343,000 


94,932,000 



Acquisition 1 

30 mining units 

Miscellaneous mining 

equipment 

Working capital^ 

Total 



5,000,135 SHORT TONS OF PRODUCT PER YEAR 



'Cost of property requi 
^Working capital equals 



$100,003,000 
21,140,000 

1,320,000 
14,688,000 



137,151,000 



$100,003 
21,684 

1,320 
15,606 



,000 
,000 

,000 
,000 



138,613,000 



$100,003,000 
22,229,000 

1,320,000 
16,551,000 



140,103,000 



$100,003,000 
23,100,000 

1,320,000 
18,063,000 



142,486.000 



red for 20-yr operation. 
90 days' operating cost. 



19 



TABLE B-2. - Estimated annual operating costs, borehole mining system 



Overburden, ft. 



50 



100 



150 



230 



1,666,590 SHORT TONS OF PRODUCT PER YEAR 



Site preparation 

Drilling, casing, and 

Operating labor 

Support labor 

Maintenance labor 

Supervisory labor 

Payroll benefits 

Payroll overhead 

Power , 

Maintenance supplies.. 

Health and safety 

Site reclamation 

Slurry transportation. 

Fixed costs 

Total 



sealing. 



$332 

1,558 

1,051 

840 

262 

430 

775 

1,034 

6,039 

331 

210 

2,975 

1,014 

2,535 



19,393 



558 
368 
200 
960 
800 
992 
786 
381 
220 
820 
152 
115 
014 
717 



083 



$332 

2,668 

1,051 

840 

262 

430 

775 

1,034 

6,205 

331 

210 

2,975 

1,014 

2,535 



20,669 



558 
628 
200 
960 
800 
992 
786 
381 
220 
820 
152 
115 
014 
717 



343 



$332 

3,778 

1,051 

840 

262 

430 

775 

1,034 

6,371 

331 

210 

2,975 

1,014 

2,535 



21,945 



558 
888 
200 
960 
800 
992 
786 
381 
220 
820 
152 
115 
014 
717 



603 



$332 

5,555 

1,051 

840 

262 

430 

775 

1,034 

6,636 

331 

210 

2,975 

1,014 

2,535 



23,987 



3,333,180 SHORT TONS OF 



PRODUCT PER 



YEAR 



Site preparation 

Drilling, casing, and sealing. 

Operating labor 

Support labor 

Maintenance labor 

Supervisory labor 

Payroll benefits 

Payroll overhead. 

Power 

Maintenance supplies 

Health and safety 

Site reclamation. 

Slurry transportation 

Fixed costs 

Total 



$665 

3,116 

2,102 

1,681 

525 

646 

1,486 

1,982 

2,078 

663 

420 

5,950 

3,042 

5,071 



116 
736 
400 
920 
600 
488 
922 
563 
440 
640 
300 
230 
041 
433 



39,433 



829 



$665 

5,337 

2,102 

1,681 

525 

646 

1,486 

1,982 

12,410 

663 

420 

5,950 

3,042 

5,071 



116 
256 
400 
920 
600 
488 
922 
563 
440 
640 
300 
230 
041 
433 



41,986 



349 



$665 

7,557 

2,102 

1,681 

525 

646 

1,486 

1,982 

12,742 

663 

420 

5,950 

3,042 

5,071 



116 
776 
400 
920 
600 
488 
922 
563 
440 
640 
300 
230 
041 
433 



44,538 



869 



$665 

11,110 

2,102 

1,681 

525 

646 

1,486 

1,982 

13,273 

663 

420 

5,950 

3,042 

5,071 



48,622 



5,000,135 SHORT TONS OF 



PRODUCT PER 



YEAR 



Site preparation 

Drilling, casing, and sealing. 

Operating labor 

Support labor 

Maintenance labor 

Supervisory labor 

Payroll benefits 

Payroll overhead 

Power 

Maintenance supplies 

Health and safety 

Site reclamation 

Slurry transportation 

Fixed costs 

Total 



$997 

4,675 

3,153 

2,522 

788 

646 

2,133 

2,844 

18,117 

995 

630 

8,924 

5,475 

7,607 



674 
104 
600 
880 
400 
488 
410 
547 
660 
460 
450 
798 
556 
706 



59,513 



733 



$997 

8,005 

3,153 

2,522 

788 

646 

2,133 

2,844 

18,615 

995 

630 

8,924 

5,475 

7,607 



674 
884 
600 
880 
400 
488 
410 
547 
660 
460 
450 
798 
556 
706 



63,342 



513 



$997 

11,336 

3,153 

2,522 

788 

646 

2,133 

2,844 

19,113 

995 

630 

8,924 

5,475 

7,607 



674 
664 
600 
880 
400 
488 
410 
547 
660 
460 
450 
798 
556 
706 



67,171 



293 



$997 

16,665 

3,153 

2,522 

788 

646 

2,133 

2,844 

19,910 

995 

630 

8,924 

5,475 

7,607 



73,297 



20 



APPENDIX C. —CONVENTIONAL MINING SYSTEM CAPITAL AND OPERATING COSTS 
TABLE C-1. - Estimated capital requirements, conventional mining systems 



Overburden, ft. 



50 



100 



150 



1,666,590 SHORT TONS OF PRODUCT PER YEAR 

Acquisition ' 

Mine equipment 

Draglines and bucket wheel excavators 



Working capital^ , 
Total. 



$33,332,000 
14,262,000 
9,479,000 
2,088,000 



59,161,000 



$33 
22 
17 
2 



,332,000 
,103,000 
,115,000 
,628,000 



75,178,000 



$33,332,000 

26,936,000 

60,610,000 

5,175,000 



126,053,000 



3,333,180 SHORT TONS OF PRODUCT PER YEAR 



Acquisition^ , 

Mining equipment , 

Draglines and bucket wheel 

Working capital^ , 

Total , 



excavators. 



$66,664,000 

24,511,000 

18,958,000 

3,600,000 



113,733,000 



$66 
28 
28 

4 



,664,000 
,798,000 
,437,000 
,158,000 



128,057,000 



$66,664,000 

36,649,000 

99,094,000 

7.722,000 



210,129,000 



5,000,135 SHORT TONS OF PRODUCT PER YEAR 

Acquisition ^ 

Mine equipment 

Draglines and bucket wheel excavators.... 



Working capital^ , 

Total 

'Cost of property required 
^Working capital equals 90 



$100,003,000 
26,566,000 
37,389,000 
4,617,000 



168,575,000 



$100 
35 
37 
5 



,003,000 
,380,000 
,916,000 
,724,000 



179,023,000 



$100,003,000 

45,807,000 

131,763,000 

10,152,000 



287,725,000 



for 20-yr operation, 
days' operating cost. 



21 



TABLE C-2. - Estimated annual operating costs, conventional mining system, 
at 1.6 million short tons of product per year' 



Overburden, ft. 



50 



100 



150 



DRAGLINE SYSTEM 



Direct: 
Power, 
Fuel. . 



Supplies 

Mobile mine support equipment 

Outside services 

Direct operating labor 

Direct production supervision. 

Maintenance labor 

Maintenance supervision 

Maintenance parts and supplies 

Replacement mine pipe 

Payroll overhead 

Indirect: 

Administrative, technical, and clerical labor... 

Administrative payroll overhead 

Facilities maintenance and supplies 

General overhead 

Fixed: 

Local taxes 

Insurance 

BUCKET WHEEL EXCAVATOR SYSTEM 
Direct: 

Power. 

Maintenance supplies 

Operating and maintenance labor 

Indirect: Administrative, technical, and clerical 

labor, facilities maintenance and supplies 

Fixed: Local taxes and insurance 

Total 



$901,938 
58,771 
328,213 
333,037 
359,293 
892,079 
380,605 
270,091 
159,648 
1,172,478 
120,972 
411,283 

397,526 
95,435 
24,638 
31,694 

2,511,152 
33,332 



NAp 
NAp 
NAp 

NAp 
NAp 



$1,005,908 

82,280 

382,532 

466,252 

359,293 

1,227,241 
520,784 
397,526 
234,339 

1,873,659 
241,944 
575,907 

514,341 

123,470 

31,859 

42,835 

2,558,546 
33,332 



NAp 
NAp 
NAp 

NAp 
NAp 



$1,005,908 

82,280 

382,532 

466,252 

359,293 

1,227,241 
520,784 
397,526 
234,339 

1,873,659 
241,944 
575,907 

514,341 

123,470 

31,859 

46,755 

2,558,546 
33,332 



1,418,549 
4,038,390 
3,003,741 

1,547,685 
309,537 



8,482,185 



10,672,048 



20,993,870 



NAp Not applicable. 

'Precise production value, 1,666,590 short tons. 



22 



TABLE C-3. - Estimated annual operating costs, conventional mining system, 
at 3.3 million short tons of product per year' 



Overburden , ft 

DRAGLINE SYSTEM 
Direct: 

Power 

Fuel 

Supplies 

Mobile mine support equipment 

Outside services 

Direct operating labor 

Direct production supervision 

Maintenance labor 

Maintenance supervision. 

Maintenance parts and supplies 

Replacement mine pipe 

Payroll overhead 

Indirect: 

Administrative, technical, and clerical labor... 

Administrative payroll overhead 

Facilities maintenance and supplies 

General overhead 

Fixed: 

Local taxes 

Insurance 

BUCKET WHEEL EXCAVATOR SYSTEM 
Direct: 

Power 

Maintenance supplies 

Operating and maintenance labor 

Indirect: Administrative, technical, and clerical 

labor, facilities maintenance and supplies 

Fixed: Local taxes and insurance 

Total 

NAp Not applicable. 

'Precise production value, 3,333,180 short tons. 



50 



100 



150 



$1,925,765 

82,280 

490,972 

466,252 

718,586 

1,227,241 
520,784 
397,526 
234,339 

1,873,659 
349,476 
575,907 

514,341 

123,470 

31,859 

45,971 

4,985,850 
66,664 



NAp 
NAp 
NAp 

NAp 
NAp 



$2,106,357 
105,788 
544,627 
599,467 
718,586 
1,562,404 
659,263 
524,961 
300,534 
2,488,121 
524,213 
737,883 

631,864 

151,648 

39,151 

61,103 

5,027,432 
66,664 



NAp 
NAp 
NAp 

NAp 
NAp 



$2,106,357 
105,788 
544,627 
599,467 
718,586 

1,562,404 
659,263 
524,961 
300,534 

2,488,121 
524,213 
737,883 

631,864 

151,648 

39,151 

68,943 

5,027,432 
66,664 



2,306,316 
6,565,727 
3,003,741 

2,172,399 
434,480 



14,630,942 



16,850,066 



31,340,569 



23 



TABLE C-4. - Estimated annual operating costs, conventional mining system, 
at 5.0 million short tons of product per year' 



Overburden, ft 

DRAGLINE SYSTEM 
Direct: 

Power 

Fuel 

Supplies 

Mobile mine support equipment 

Outside services 

Direct operating labor 

Direct production supervision 

Maintenance labor 

Maintenance supervision 

Maintenance parts and supplies 

Replacement mine pipe 

Payroll overhead 

Indirect: 

Administrative, technical, and clerical labor... 

Administrative payroll overhead 

Facilities maintenance and supplies 

General overhead 

Fixed: 

Local taxes 

Insurance 

BUCKET WHEEL EXCAVATOR SYSTEM 
Direct: 

Power 

Maintenance supplies 

Operating and maintenance labor 

Indirect: Administrative, technical, and clerical 

labor, facilities maintenance and supplies. 

Fixed: Local taxes and insurance 

Total 

NAp Not applicable. 

'Precise production value, 5,000,135 short tons. 



50 



100 



150 



$2,994,996 

82,280 

635,591 

466,252 

1,077,878 

1,227,241 

520,784 

397,526 

234,339 

1,873,659 

430,124 

575,907 

514,341 

123,470 

31,859 

52,977 

7,415,325 
100,003 



NAp 
NAp 
NAp 

NAp 
NAp 



$3,265,884 

129,297 

742,901 

732,681 

1,077,878 

1,897,566 

797,734 

652,396 

369,072 

3,101,507 

860,247 

898,472 

749,382 

179,852 

46,433 

79,361 

7,498,490 
100,003 



NAp 
NAp 
NAp 

NAp 
NAp 



$3,265,884 

129,297 

742,901 

732,681 

1,077,878 

1,897,566 

797,734 

652,396 

369,072 

3,101,507 

860,247 

898,472 

749,382 

179,852 

46,433 

91,121 

7,498,490 
100,003 



3,057,864 
8,705,272 
3,003,741 

2,701,258 
540,252 



18,754,552 



23,179,156 



41,199,303 



24 



APPENDIX D.~BENEFICIATION SYSTEM CAPITAL AND OPERATING COSTS 

TABLE D-1, - Estimated capital requirements, benef iciation 
system 



Annual mining rate, 
short tons of product 



Mill plant 



Working 
capital ^ 



Total 



1,666,590. 
3,333,180. 
5,000,135. 



$35,500,000 
53,808,000 
68,628,000 



$702,000 
1,314,000 
1,890,000 



$36,202,000 
55,122,000 
70,518,000 



Working capital equals 90 days' operating cost. 



TABLE D-2. - Estimated annual operating costs, benef iciation system 



Short tons of product | 1,666,590 [ 3,333,180 



5,000,135 



ANNUAL COST 



Power and labor. 

Reagents. 

Fixed costs 

Total 



$949,956 

1,433,268 

447,479 



2,830,703 



$1,533,263 

2,866,535 

894,959 



5,294,757 



$2,050,055 
4,300,116 
1,342,536 



7.692,707 



COST PER SHORT TON OF PRODUCT' 



Power and labor 

Reagents 

Fixed costs 

Total 

'Rounded to the nearest cent. 



$0.57 
.86 
.27 



1.70 



$0.46 
.86 
.27 



1.59 



$0.41 
.86 
.27 



1.54 



25 



APPENDIX E.— CASH FLOW ANALYSIS 

TABLE E-1. - Cash flow analysis at 50-ft overburden and 1.6 million short tons 
of product per year 

(Based on annual revenue of $49,995,506) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


0^ 


$56,998,666 


-$56,998,666 





$56,998,666 


-$56,998,666 





1 


24,801,333 


-4,621,091 





38,364,333 


-10,131,711 





2 





18,593,989 








25,020,969 





3 





18,939,770 








25,366,750 





4 





18,939,770 








25,366,750 


3.43 


5 





18,939,770 


4.88 





25,366,750 


10.27 


6 





18,939,770 


9.28 





25,366,750 


14.32 


7 





18,939,770 


12.15 





25,366,750 


16.91 


8 





18,939,770 


14.11 





25,366,750 


18.63 


9 





18,915,664 


15.49 





24,585,359 


19.79 


10 





18,915,664 


16.49 





24,585,359 


20.62 


11 


440,000 


17,326,678 


17.17 


14,262,000 


11,875,593 


20.92 


12 





17,722,678 


17.70 





24,711,393 


21.39 


13 





17,722,678 


18.11 





24,711,393 


21.74 


14 





17,722,678 


18.42 





24,711,393 


22.00 


15 





17,722,678 


18.67 





24,711,639 


22.20 


16 





17,170,993 


18.86 





24,088,639 


22.36 


17 





16,825,212 


19.00 





23,742,858 


22.47 


18 





16,479,432 


19.12 





23,397,077 


22.56 


19 





16,455,325 


19.21 





22,615,686 


22.62 


203 


-9,823,000 


26,278,325 


19.32 


-10,139,000 


32,754,686 


22.70 



1 Discounted eash flow rate of return at $30 per short ton of phosphate rock product, 

2Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 20. 



26 



TABLE E-2. - Cash flow analysis at 100-ft overburden and 1.6 million short tons 
of product per year 

(Based on annual revenue of $49,995,506) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


02 


$56,998,666 


-$56,998,666 





$56,998,666 


-$56,998,666 





1 


25,297,333 


-5,749,057 





54,381,333 


-25,071,775 





2 





17,943,924 








24,550,205 





3 





18,289,705 








24,895,986 





4 





18,289,705 








24,895,986 





5 





18,289,705 


3.61 





24,895,986 


5.08 


6 





18,289,705 


8.16 





24,895,986 


9.87 


7 





18,289,705 


11.12 





24,895,986 


12.93 


8 





18,289,705 


13.15 





24,895,986 


14.98 


9 





18,265,598 


14.56 





23,685,000 


16.35 


10 





18,265,598 


15.63 





23,685,000 


17.34 


11 


440,000 


16,601,714 


16.34 


22,103,000 


4,235,581 


17.48 


12 





16,997,714 


16.89 





24,128,281 


18.09 


13 





16,997,714 


17.32 





24,128,281 


18.55 


14 





16,997,714 


17.65 





24,128,281 


18.90 


15 





16,997,714 


17.91 





24,128,281 


19.17 


16 





16,440,738 


18.11 





23,282,417 


19.38 


17 





16,094,957 


18.26 





22,936,636 


19.54 


18 





15,749,176 


18.38 





22,590,855 


19.66 


19 





15,725,070 


18.48 





21,379,869 


19.75 


203 


-10,156,000 


25,881,070 


18.61 


-13,011,000 


34,390,869 


19.87 


iDiscoun 


ted cash flovg 


rate of retur 


n at $30 per 


short ton of 


phosphate rock product. 



^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 20. 



27 



TABLE E-3. - Cash flow analysis at 150-ft overburden and 1.6 million short tons 
of product per year 

(Based on annual revenue of $49,995,506) 





Borehole mining 


Conventional mini 


ng 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


02 


$56,998,666 


-$56,998,666 





$56,998,666 


-$56,998,666 





1 


25,794,333 


-6,877,890 





105,256,333 


-80,195,134 





2 





17,293,891 








25,127,728 





3 





17,639,672 








22,109,579 





4 





17,639,672 








21,132,638 





5 





17,639,672 


2.31 





21,132,638 





6 





17,639,672 


7.00 





21,132,638 





7 





17,639,672 


10.07 





21,132,638 





8 





17,639,672 


12.17 





21,132,638 


2.35 


9 





17,615,565 


13.66 





19,656,906 


4.57 


10 





17,615,565 


14.75 





19,656,906 


6.23 


11 


440,000 


15,895,508 


15.49 


26,936,000 


-4,420,477 


5.91 


12 





16,291,508 


16.06 





19,821,923 


7.16 


13 





16,291,508 


16.51 





19,821,923 


8.12 


14 





16,291,508 


16.86 





19,821,923 


8.88 


15 





16,291,508 


17.13 





19,821,923 


9.48 


16 





15,729,207 


17.35 





17,705,118 


9.91 


17 





15,383,426 


17.51 





17,359,337 


10.26 


18 





15,037,645 


17.64 





17,013,556 


10.55 


19 





15,013,539 


17.75 





15,537,825 


10.77 


203 


-10,489,000 


25,502,539 


17.89 


-20,875,000 


36,412,825 


11.19 



^Discounted cash flow rate of return at $30 per short ton of phosphate rock product, 

^Year equals total preproduction years. 

3Equipment value and working capital salvaged in year 20. 



28 



TABLE E-4. - Cash flow analysis at 50-ft overburden and 3.3 million short tons 
of product per year 

(Based on annual revenue of $99,991,012) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


02 


$102,536,000 


-$102,536,000 





$102,536,000 


-$102,536,000 





1 


43,943,000 


-4,492,214 





66,319,000 


-9,849,125 





2 





36,683,963 








50,853,452 





3 





37,208,040 








51,377,529 





4 





37,208,040 


1.00 





51,377,529 


8.55 


5 





37,208,040 


7.74 





51,377,529 


14.64 


6 





37,208,040 


11.82 





51,377,529 


18.24 


7 





37,208,040 


14.47 





51,377,529 


20.51 


8 





37,208,040 


16.27 





51,377,529 


22.01 


9 





37,159,827 


17.53 





50,034,626 


23.01 


10 





37,159,827 


18.43 





50,034,626 


23.71 


11 


880,000 


33,981,855 


19.05 


24,511,000 


28,156,710 


24.00 


12 





34,773,855 


19.52 





50,216,610 


24.38 


13 





34,773,855 


19.87 





50,216,610 


24.66 


14 





34,773,855 


20.15 





50,216,610 


24.87 


15 





34,773,855 


20.36 





50,216,610 


25.02 


16 





33,837,971 


20.52 





49,138,586 


25.14 


17 





33,313,894 


20.65 





48,614,510 


25.22 


18 





32,789,817 


20.74 





48,090,433 


25.29 


19 





32,741,604 


20.82 





46,747,530 


25.33 


203 


-18,001,000 


50,742,604 


20.91 


-17,094,000 


63,841,530 


25.38 



'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, 

^Year equals total preproduction years. 

3Equipment value and working capital salvaged in year 20. 



29 



TABLE E-5. - Cash flow analysis at 100-ft overburden and 3.3 million short tons 
of product per year 

(Based on annual revenue of $99,991,012) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


0^ 


$102,536,000 


-$102,536,000 





$102,536,000 


-$102,536,000 





1 


44,936,000 


-6,749,045 





80,643,000 


-23,445,615 





2 





35,383,832 








50,204,362 





3 





35,907,909 








50,728,439 





4 





35,907,909 








50,728,439 


5.32 


5 





35,907,909 


6.44 





50,728,439 


12.00 


6 





35,907,909 


10.66 





50,728,439 


15.94 


7 





35,907,909 


13.40 





50,728,439 


18.42 


8 





35,907,909 


15.27 





50,728,439 


20.08 


9 





35,859,696 


16.58 





49,150,680 


21.18 


10 





35,859,696 


17.53 





49,150,680 


21.96 


11 


880,000 


32,531,928 


18.17 


28,798,000 


23,536,973 


22.24 


12 





33,323,928 


18.66 





49,455,173 


22.67 


13 





33,323,928 


19.04 





49,455,173 


22.99 


14 





33,323,928 


19.33 





49,455,173 


23.24 


15 





33,323,928 


19.56 





49,455,173 


23.42 


16 





32,377,460 


19.73 





48,100,176 


23.55 


17 





31,853,383 


19.86 





47,576,099 


23.66 


18 





31,329,306 


19.97 





47,052,022 


23.73 


19 





31,281,093 


20.05 





45,474,264 


23.79 


203.... 


-18,668,000 


49,949,093 


20.15 


-19,458,000 


64,932,264 


23.86 


'Discoun 


ted cash flow 


rate of returi 


1 at $30 per 


short ton of 


phosphate rock product. 



^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 



20. 



30 



TABLE E-6. - Cash flow analysis at 150-ft overburden and 3.3 million short tons 
of product per year 

(Based on annual revenue of $99,991,012) 



Borehole mining 



Conventional mining 



Year 



Capital 
expenditure 



02.... 

1 

2 

3 

4 

5 

6 

7...., 

8 

9 

10 

11...., 
12...., 

13 

14 

15 

16 

17 

18 

19 

203..., 



Cash flow 



Continuous 
rate of 
return, ' 
pet 



Capital 
expenditure 



Cash flow 



Continuous 
rate of 
return, ' 
pet 



$102,536,000 
45,929,000 









880,000 








-19,334,000 



-$102,536,000 
-9,005,843 
34,083,734 
34,607,81 
34,607,81 
34,607,81 
34,607,81 
34,607,81 
34,607,81 
34,559,598 
34,559,598 
31,119,483 
31,911,483 
31,911,483 
31,911,483 
31,911,483 
30,954,398 
30,430,321 
29,906,244 
29,858,031 
49,192,031 













5.10 

9.47 
12.31 
14.25 
15.62 
16.61 
17.27 
17.79 
18.19 
18.50 
18.74 
18.92 
19.07 
19.18 
19.27 
19.39 



$102,536,000 
162,715,000 









36,649,000 








-31,657,000 



-$102,536,000 
-102,945,041 
45,642,310 
45,808,300 
45,808,300 
45,808,300 
45,808,300 
45,808,300 
45,808,300 
43,800,399 
43,800,399 
10,801,954 
43,786,054 
43,786,054 
43,786,054 
43,786,054 
40,366,437 
39,842,360 
39,318,283 
37,310,382 
68,967,382 















2.77 

6.68 

9.32 
11.11 
12.41 
12.66 
13.49 
14.13 
14.62 
15.01 
15.29 
15.52 
15.70 
15.84 
16.05 



'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, 

^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 20. 



31 



TABLE E-7. - Cash flow analysis at 50-ft overburden and 5.0 million short tons 
of product per year 

(Based on annual revenue of $149,986,517) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


02 


$145,755,000 


-$145,755,000 





$145,755,000 


-$145,755,000 





1 


61,914,000 


-3,324,061 





93,338,000 


-7,787,912 





2 





54,724,763 








77,535,412 





3 





55,393,187 








78,203,836 


0.44 


4 





55,393,187 


2.75 





78,203,836 


11.29 


5 





55,393,187 


9.24 





78,203,836 


17.01 


6 





55,393,187 


13.16 





78,203,836 


20.38 


7 





55,393,187 


15.70 





78,203,836 


22.49 


8 





55,393,187 


17.41 





78,203,836 


23.88 


9 





55,320,867 


18.61 





76,748,375 


24.80 


10 





55,320,867 


19.47 





76,748,375 


25.45 


11 


1,320,000 


50,553,909 


20.04 


26,566,000 


52,721,578 


25.76 


12 





51,741,909 


20.48 





76,630,978 


26.10 


13 





51,741,909 


20.82 





76,630,978 


26.34 


14 





51,741,909 


21.07 





76,630,978 


26.52 


15 





51,741,909 


21.27 





76,630,978 


26.66 


16 





50,455,775 


21.42 





74,870,050 


26.75 


17 





49,787,351 


21.53 





74,201,627 


26.82 


18 





49,118,927 


21.62 





73,533,203 


26.88 


19 





49,046,608 


21.69 





72,077,743 


26.92 


203 


-25,820,000 


74,866,608 


21.77 


-22,424,000 


94,510,743 


26.96 



'Discounted eash flow rate of return at $30 per short 

^Year equals total preproduction years. 

3Equipment value and working capital salvaged in year 



ton of phosphate rock product. 



20. 



32 



TABLE E-8. - Cash flow analysis at 100-ft overburden and 5.0 million short tons 
of product per year 

(Based on annual revenue of $149,986,517) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, 1 
pet 


expenditure 




return, ' 
pet 


0^ 


$145,755,000 


-$145,755,000 





$145,755,000 


-$145,755,000 





1 


63,376,000 


-6,625,651 





103,786,000 


-19,106,615 





2 





52,830,773 








75,730,609 





3 





53,499,196 








76,399,033 





4 





53,499,196 


1.27 





76,399,033 


9.01 


5 





53,499,196 


7.96 





76,399,033 


15.10 


6 





53,499,196 


12.01 





76,399,033 


18.68 


7 





53,499,196 


14.64 





76,399,033 


20.94 


8 





53,499,196 


16.42 





76,399,033 


22.42 


9 





53,426,877 


17.67 





74,460,651 


23.41 


10 





53,426,877 


18.57 





74,460,651 


24.11 


11 


1,320,000 


48,435,225 


19.17 


35,380,000 


42,759,481 


24.40 


12 





49,623,225 


19.63 





74,601,481 


24.77 


13 





49,623,225 


19.99 





74,601,481 


25.04 


14 





49,623,225 


20.26 





74,601,481 


25.24 


15 





49,623,225 


20.46 





74,601,481 


25.39 


16 





48,321,182 


20.62 





72,825,164 


25.50 


17 





47,652,758 


20.74 





72,156,741 


25.59 


18 





46,984,334 


20.84 





71,488,317 


25.65 


19 





46,912,015 


20.92 





69,549,935 


25.69 


203 


-26,792,000 


73,704,015 


21.01 


-25,346,000 


94,895,935 


25.74 



'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, 

^Year equals total preproduction years. 

3Equipment value and working capital salvaged in year 20. 



33 



TABLE E-9. - Cash flow analysis at 150-ft overburden and 5.0 million short tons 
of product per year 

(Based on annual revenue of $149,986,517) 





Borehole mining 


Conventional mining 








Continuous 






Continuous 


Year 


Capital 


Cash flow 


rate of 


Capital 


Cash flow 


rate of 




expenditure 




return, ' 
pet 


expenditure 




return, ' 
pet 


02 


145,755,000 


-$145,755,000 





$145,755,000 


-$145,755,000 





1 


64,866,000 


-10,011,315 





212,488,000 


-123,280,186 





2 





50,880,609 








69,831,638 





3 





51,549,032 








70,500,062 





4 





51,549,032 








70,500,062 





5 





51,549,032 


6.60 





70,500,062 


1.28 


6 





51,549,032 


10.80 





70,500,062 


6.77 


7 





51,549,032 


13.53 





70,500,062 


10.25 


8 





51,549,032 


15.38 





70,500,062 


12.58 


9 





51,476,713 


16.68 





67,990,429 


14.16 


10 





51,476,713 


17.63 





67,990,429 


15.31 


11 


1,320,000 


46,316,540 


18.25 


45,807,000 


26,521,260 


15.65 


12 





47,504,540 


18.74 





67,747,560 


16.33 


13 





47,504,540 


19.11 





67,747,560 


16.86 


14 





47,504,540 


19.40 





67,747,560 


17.26 


15 





47,504,540 


19.62 





67,747,560 


17.57 


16 





46,186,589 


19.79 





63,229,012 


17.80 


17 





45,518,165 


19.93 





62,560,588 


17.98 


18 





44,849,741 


20.03 





61,892,164 


18.12 


19 





44,777,422 


20.11 





59,382,532 


18.23 


203 


-27,792,000 


72,569,422 


20.22 


-41,244,000 


100,626,532 


18.38 



'Discounted eash flow rate of return at $30 per short 

^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 



ton of phosphate rock product. 



20. 



34 



TABLE E-10. - Cash flow analysis, borehole mining, at 230-ft overburden and 1.6 million short tons 
of product per year 

(Based on annual revenue of $49,995,506) 



Year 


Capital 


Cash flow 


Continuous rate 


Year 


Capital 


Cash flow 


Continuous rate 




expenditure 




of return, ' pet 




expenditure 




of return, ' pet 


0^... 


$56,998,666 


-$56,998,666 





U 


440,000 


14,743,062 


14.08 


1.... 


26,588,333 


-8,682,988 





12 





15,139,062 


14.70 


2.... 





16,253,793 





13 





15,139,062 


15.18 


3 





16,599,573 





14 





15.139,062 


15.56 


4 





16,599,573 





15 





15,139,062 


15.86 


5 





16,599,573 


0.14 


16 





14,568,288 


16.10 


6 





16,599,573 


5.08 


17 





14,222,507 


16.28 


7 





16,599,573 


8.32 


18 





13,876,726 


16.42 


8.... 





16,599,573 


10.55 


19 





13,852,620 


16.54 


9 





16,575,467 


12.13 


203... 


-11,022,000 


24,874.620 


16.72 


10 





16,575,467 


13.30 











'Discounted cash flow rate of return at $30 per short ton of phosphate rock product. 

^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 20. 

TABLE E-11. - Cash flow analysis, borehole mining, at 230-ft overburden and 3.3 million short tons 
of product per year 

(Based on annual revenue of $99,991,012) 



Year 


Capital 


Cash flow 


Continuous rate 


Year 


Capital 


Cash flow 


Continuous rate 




expenditure 




of return, ' pet 




expenditure 




of return, ' pet 


0^... 


$102,536,000 


-$102,536,000 





11 


880.000 


28,814,625 


15.80 


1 


47,518,000 


-12,616,907 





12 





29,606,625 


16.36 


2 





32,003,570 





13 





29,606.625 


16.79 


3 





32,527,647 





14 





29,606,625 


17.13 


4 





32,527,647 





15 





29,606,625 


17.39 


5 





32.527,647 


2.87 


16 





28,632,560 


17.60 


6 





32,527,647 


7.48 


17 





28,108.483 


17.76 


7 





32,527,647 


10.49 


18.... 





27,584.406 


17.88 


8 





32,527,647 


12.56 


19 





27,536,193 


17.99 


9 





32,479,434 


14.20 


203... 


-20.400,000 


47,936,193 


18.13 


10 





32,479,434 


15.09 











'Discounted cash flow rate of return at $30 per short ton of phosphate rock product. 

^Year equals total preproduction years. 

^Equipment value and working capital salvaged in year 20. 

TABLE E-12. - Cash flow analysis, borehole mining, at 230-ft overburden and 5.0 million short tons 
of product per year 

(Based on annual revenue of $149,986,517) 



Year 


Capital 


Cash flow 


Continuous rate 


Year 


Capital 


Cash flow 


Continuous rate 




expenditure 




of return, ' pet 




expenditure 




of return, ' pet 


0^... 


$145,755,000 


-$145,755,000 





11 


1,320,000 


42,859,237 


16.75 


1.... 


67.249.000 


-15,427,477 





12 





44,047,237 


17.27 


2 





47,760,347 





13 





44,047,237 


17.68 


3 





48.428.770 





14 





44,047,237 


17.99 


4 





48,428,770 





15 





44,047,237 


18.24 


5.... 





48,428,770 


4.34 


16 





42,703,832 


18.43 


6 





48,428,770 


8.78 


17 





42,035,408 


18.58 


7 





48,428,770 


11.68 


18 





41,366,984 


18.70 


8 





48,428,770 


13.66 


19 





41,294,665 


18.79 


9 





48.356,451 


15.06 


203... 


-29.391.000 


70,685,665 


18.92 


10 





48,356,451 


16.07 











'Discounted cash flow rate of return at $30 per shor 
^Year equals total preproduction years. 
3Equipment value and working capital salvaged in yea 



t ton of phosphate rock product, 
r 20. 



INT.-BU.OF MINES, PGH., PA. 267B9 



9^63 



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